The invention relates to a method and apparatus for feeding a thread without twists into a textile machine, such as a weaving machine.
According to a method known from EP 03 96 902A (U.S. Pat. No. 5,069,395A), thread is supplied from a storage bobbin to the thread feeding device in twist-free condition by driving the storage bobbin with a rotation corresponding to the thread speed in the thread feeding device. In the interior of the thread feeding device, the thread passes the hollow central shaft and the winding element (which protrudes outwardly from the central shaft) before the thread is laid into adjacent windings on the storage drum. The thread is withdrawn by the textile machine from the thread windings and overhead of the storage drum, with an orbiting thread withdrawal point first inwardly and then further axially. Due to the function, a twist is generated in the thread with each rotation of the central shaft, i.e., a twist of 360xc2x0 in the rotational direction of the central shaft. During withdrawal of a complete winding from the storage drum a twist is also formed, i.e. a twist of 360xc2x0, however, in the opposite direction of rotation. This means, theoretically, that each twist formed during winding-on should be removed during withdrawal such that the thread should run without twists into the textile machine. However, the transition from the central shaft into the winding element forms a mechanical obstacle in the thread running path. Since the thread is supported on the storage drum and the winding element is rotating in relation to the storage drum circumference, the winding element generates a pulling stress in the thread. Among other factors, the influence of the pulling stress in a band-shaped thread leads in practice to a phenomenon at the obstacle, which phenomenon disturbs the equilibrium between the generated twists and the twists removed during winding-off. Each formed twist is not conveyed downstream immediately, but one or several twists may accidentally be withheld upstream of the transition. The withheld twists may even form backwardly opposite to the thread running direction and first will pass the obstacle of the transition with a delay and/or in groups of several twists, respectively. In the event that a twist is missing in a winding on the storage drum, later during withdrawal of the same winding a twist in the opposite direction will be generated and then will be conveyed into the textile machine, or in the case that there are several twists in one and the same winding on the storage drum, then during withdrawal of the same winding only one twist is removed, while the remaining twists will be conveyed into the textile machine. Despite considerable efforts to supply the thread from the thread storage bobbin into the thread feeding device without any twists, fabric faults and function disturbances caused by twists cannot be avoided which twists originate from the operation of the thread feeding device only.
It is an object of the invention to provide a method of the kind as aforementioned as well as a thread feeding device for carrying out the method, by which fabric faults and function disturbances caused by twists originating from the operation of the thread feeding device can be avoided.
This object can be achieved by stationarily supporting the thread against twisting within the central shaft, so that twists generated during the functioning of the thread feeding device are prevented from forming within the central shaft, and so that one 360xc2x0 twist is formed in each winding on the storage drum. In this regard, the thread is mechanically supported by a stationary thread guiding member or a band guiding gap.
When, according to the method of the present invention, during operation of the thread feeding device each generated twist is formed regularly and in correspondence with the rotation of the central shaft and immediately is conveyed into the first winding on the storage drum, and if a backward formation of one or of several twists opposite to the thread running direction from the location of transition from the central shaft into the winding element is hindered, the balance between twists generated during winding-on and twists removed during the withdrawal will be maintained stably. Thanks to the mechanical support of the running thread which prevents a thread rotation in the rotating central shaft, one twist is reliably formed in each winding on the storage drum, which twist then is removed during withdrawal of the same winding. The result is that the thread runs completely without twists into the textile machine, provided that the thread is supplied without twists to the thread feeding device.
In the thread feeding device, the incoming thread is supported stationarily by using the thread band cross-section to prevent thread rotation, at least upstream of the transition from the central shaft into the winding element, and the thread is mechanically guided such that the thread first can be twisted after exiting from the band guiding gap. The gap provides, due to its shape and due to its position at the transition, a check valve function and prevents a twist from starting to form earlier and tending to move backwards opposite to the thread running direction or prevents several twists from being formed and withheld. The stationary thread guiding gap assures that each twist formed during the rotation of the central shaft is formed at a predetermined location and is instantly conveyed through the winding element and into the winding on the storage drum. In the thread winding package on the storage drum each winding will contain only one twist. When withdrawing a winding overhead of the storage drum this twist is removed. In this case it is of importance that the thread is not only supported against pre-twisting during the operation of the thread feeding device, but also in a stop condition of the thread feeding device, because even then a twist may have a tendency to extend in the direction of the least resistance, i.e. opposite to the thread running direction and back into the central shaft, and to remain withheld at the transition with the following restarting of the operation of the thread feeding device.
Furthermore, it is expedient in terms of the method to support the thread during each revolution of the central shaft by a form-fit in order to control the formation of the twist and the proper transport of each twist. This avoids a twist remaining at the obstacle formed by the transition while the thread is running.
The band guiding gap is formed in the thread feeding device as a slot nozzle penetrating into the central shaft. The dimension of the slot nozzle in the direction of the slot exceeds the width of the bandshaped thread, while the gap width exceeds the thickness of the band-shaped thread, preferably only slightly, in order to assure a reliable safety against twisting of the thread and low thread passing resistance.
In a structurally simple way, the band guiding gap is provided at the free end of a carrier insert which penetrates from the thread inlet side into the central shaft, or which even may be formed by the free end of the carrier insert. The carrier insert is stationarily supported exteriorly of the central shaft at a housing wall of the thread feeding device, such that forces resulting from the guidance and deflection of the thread into the winding element are transmitted via the carrier insert to the outer side and are taken up by the housing wall. The carrier insert should not contact the rotating central shaft.
Forming the carrier insert as a rigid tube assures that the thread will not be caught or entangled along the thread running path to the band guiding gap. The band guiding gap may be formed as a tube end which is squeezed flat.
Alternatively, the slot nozzle forming the band guiding gap may be provided replaceably at the carrier insert. Depending on the kind of thread, i.e. the band width of the thread, the band thickness and the structure of the band (smooth, rough, or with fibres), a suitably sized slot nozzle will be used.
Alternatively, the slot nozzle may be replaced together with the carrier insert, e.g., if it is necessary to change from one yarn quality to another significantly different yarn quality.
The axial penetration depth of the band guiding gap into the central shaft should be adjustable in order to allow positioning of the band guiding gap in an optimum axial position in relation to the transition from the central shaft into the winding element.
In order to minimize the moving resistance of the thread in the band guiding gap, the band guiding gap should consist of a material which has good sliding properties and is wear resistant.
Expediently, the band guiding gap additionally has a guiding section of essentially constant cross-section. Advantageously, the band guiding gap is formed with a somewhat widened exit mouth.
In order to assure that one twist is formed with each revolution of the central shaft, a twist recess is provided at the transition. The twist recess rotates with the central shaft and acts upon the thread with a form-fit. The twist recess moderates the deflection of the thread and assists in a form-fit fashion during the revolution of the central shaft for properly forming the twists.
Expediently, the twist recess is located in the inner side of the knee between the hollow inner channel of the central shaft and a tube channel of the winding element. The thread exiting under deflection into the tube channel of the winding element is gripped by the recess and is taken along in the rotating direction to properly form the twists.
In order to assure a defined thread control, an eyelet may be provided in the transition, which eyelet is either completely closed or is only partially closed in the circumferential direction. The twist recess may be formed in the eyelet. The partial eyelet may extend essentially only over the circumferential width of the twist recess.
The twist recess may be a simple to manufacture V-shaped cut-out with a bottom, the bottom substantially bisecting the deflection angle between the central shaft and the winding element. This assures a mild deflection of the thread and moderates the influence of the obstacle constituted by the transition.
For easy mounting, the carrier insert may be fixed to the housing wall with the help-of a fastening part. The fastening part may have the shape of a cap, in order to guarantee a stable support. The cap may define a receiving cavity for a sensor which may be useful for other tasks in this portion of the thread feeding device.